With the support of NINCDS grant1R01NS15167(4/1/79-3/31/82) we have developed and successfully tested methods that provide a capability for the simultaneous recording of spike activity from up to 50 meurons in culture and that allow the surgical alteration of of chaotic networks into simple, mappaple networks within closed culture chambers. The methods are based on two new techniques. the utilization of photoetched, laser de-insulated multimicroelectrode surfaces and the application of UV laser microbeam cell surgery. With the funds requested in this proposal, we plan to (1) improve the technology; (2) define the requirements for a realistic data analysis; and (3) systematically apply these methods to the investigation of the characteristics of spontaneous or evoked activity in small mammalian CNS circuits in culture. For reasons of simplicity and spontaneous activity, we will concentrate our efforts on embryonic mouse spinal cord tissue. Starting with the analysis of activity in 50 mum tissue fragments, we will (I) correlate fragment structure on the LM and EM level with long term electrophysiological behavior; (2) study interactions between tissue micro-fragments by laser transection of interconnections during simultaneous recording; and (3) gradually reduce the size of the microfragments until two dimensional networks can be discerned with phase contrast microscopy. Laser cell surgery will be used to further simplify the two dimensional networks by removing neurons not situated near recording craters, to control glia cells, and to transect neurties until and optically defined network emerges. The network will be maintained at a specific pattern or altered during recording to establish the influence of specific cell processes. It is our immediate goal to establish technical and neurobiological procedures that yield reproducible network characteristics. It is our long range goal to investigate signal processing and storage with these new methods.